The present invention generally relates to a control device in use with an image recording apparatus for visually outputting an image, and more particularly to a control device for causing an image recording apparatus to output graphic data as generated by a computer, e.g., a host computer.
The image recording apparatus, which visually outputs the graphic data (vector data) as is generated by and supplied from a computer (host computer), comes in two varieties, an electrostatic plotter and Xerography plotter. The electrostatic plotter forms an electrostatic latent image on an electrostatic recording paper, applies a subsequent developing process to the latent image to visualize it, and finally records on an ordinary paper. The Xerography plotter (referred to as an XP type plotter) forms an electrostatic latent image on a photosensitive drum, and transforms the latent image into a visible image, and finally transfers it on an ordinary paper. Some types of the image recording apparatus are provided with recording papers of different sizes which are selectively used in accordance with the sizes of output visible images. Such types of the image recording apparatus includes an XP type plotter which is provided with a plurality of trays respectively containing recording papers of different sizes.
A conventional control device for controlling the image recording apparatus, when determining that the image recording apparatus is normally operable, transfers the graphic data to the image recording apparatus, and causes it to output the graphic data (visible image). In this case, a host computer generates graphic data (vector data), and a data converting unit converts it into graphic data (raster image data) and transfers the graphic data to the control device.
When a malfunction (for example, paper jamming) occurs in the image recording apparatus, the control device detects the malfunction and informs the host computer of the trouble.
When receiving data indicating the malfunction (trouble-indicating data), the host computer immediately stops the transfer of the data to the image recording apparatus, and does not send any further data to the recording apparatus until the image recording apparatus is cured of the trouble and the host computer receives data indicating the cure from the control device.
As just mentioned, in an image recording system incorporating the conventional control device, when the control device detects a trouble (e.g., paper jamming) in the image recording apparatus, it immediately sends the trouble-indicating data to the host computer. Upon receipt of the trouble-indicating data, the host computer stops the transfer of the graphic data to the image recording apparatus.
The image recording system thus operable has such a serious problem that during a period from an instant that the control device sends the trouble-indicating data in the image recording apparatus to the host computer till the host computer receives it, the graphic data transferred from the host computer are sometimes lost, which the data is, for example, the data being currently converted to the raster image data by the data converting unit. After the malfunction is removed, the host computer starts again the supply of the succeeding graphic data to the image recording apparatus. The image recording apparatus produces a visible image on the basis of the graphic data. The visible image thus formed inevitably contains a missing part, if the data is lost.
Additionally in the conventional image recording system, the host computer must retain the graphic data, which is to be transferred, until the image recording apparatus is restored to the normal state. During this period, the host computer, therefore, cannot engage in executing of other jobs. This implies a poor utilization of the host computer.